Summary: This proposal is focused on evaluating the anti-cancer efficacy of glycyrrhizin (GLY), a natural compound present in licorice as a candidate agent against castrate resistant prostate cancer (CRPC) in pre-clinical settings. GLY is reported to have several pharmacological properties including anti-cancer activity. However, the chemotherapeutic benefits of GLY has not yet evaluated against prostate cancer (PCa). Our preliminary studies have shown that GLY can target androgen receptor (AR) positive CRPC cells. In addition, our studies showed that GLY activates Placental bone morphogenic protein (PLAB) to inhibit AR positive PCa colony formation while simultaneously inhibiting High Mobility Group Box 1 (HMGB1), Receptor for Advanced Glycation End products (RAGE) and androgen receptor (AR) expression. Inappropriate activation of AR has been suggested to play a major role in the progression of lethal CRPC. Studies have also shown that PI3K/Akt pathway can inactivate glycogen synthase kinase 3 beta (GSK3?) to promote CRPC development. Based on our preliminary results and previous work, we hypothesize that GLY targets PI3K/Akt to activate GSK3?-PLAB pro- apoptotic signaling and disrupt the molecular cross talk of HMGB-RAGE and AR signaling in PCa cells. The overall objective of this proposal is to evaluate the underlying anti-cancer mechanisms of GLY and its anti-cancer efficacy using in vitro cell culture system and experimental in vivo CRPC model. This proposal has two specific aims. In Aim 1, we will delineate the anti-cancer mechanisms of GLY using AR positive CRPC cells C4-2B and 22Rv1. This aim is designed to determine how GLY activates PLAB and how PLAB antagonizes HMGB1-RAGE-AR pro-survival signaling in CRPC cells using biochemical, pharmacological, and gene silencing approaches. In Aim 2, we will determine whether GLY administration inhibits CRPC and whether anti-cancer activity of GLY dependent on PLAB in an experimental intratibial injection model of nude mice using C4-2B RFP cells. In this aim, GLY will be orally administered to test the inhibition of C4-2B RFP derived tumors in the tibae of nude mice. We will also determine whether PLAB is required for GLY to inhibit tumor growth of PLAB knockout C4-2B RFP cells and analyze whether PLAB deletion/overexpression impact the ability of CRPC cells to form tumor growth in the tibiae of nude mice. Immunohistochemistry will be performed to determine the effects of GLY on the expression of Akt, GSK3?, PLAB, HMGB1, RAGE and AR in the tumor tissue samples. Our proposed study is timely as new Akt inhibitors are currently being explored in the clinic for treatment of solid tumors. Results obtained upon successful completion of these proposed specific aims will yield valuable molecular insights in developing GLY as a potential dietary agent that will help design better treatment strategies for effective CRPC management.